This invention relates to a spin system for thermoplastic yarns as well as a multiple gear pump with several pairs of gears. Such a spin system and multiple gear pump are known from U.S. Pat. No. 3,502,033, as well as DE 19 08 207. In the spinning of thermoplastic yarns, which consist of individual filaments, the thermoplastic material, for example, polyethylene therephthalate, nylon 6, and nylon 6.6, are melted by an extruder, mixed, and then extruded under a high pressure from the main melt flow. This main melt flow is subsequently divided into several partial melt flows. Each partial melt flow is advanced to a spinneret, from which a plurality of filaments is spun. Thereafter, bundles of filaments are combined to yarns.
For the quality of the product, it is of decisive importance that the filaments between one another have the same properties. For this reason, special importance is attached to the temperature control in the melt line, which guides the main melt flow, and in the so-called spin head, in which the main melt flow is divided into partial melt flows, and in which the partial melt flows are transported to the spinnerets. Likewise of great importance is the uniform advance of all partial melt flows. For this reason, it is customary to install a multiple gear pump in the spin head. This multiple gear pump receives the main melt flow on the one hand. In the pump, the melt main flow is divided into partial melt flows. The multiple gear pump possesses several individual pumps, which serve each the purpose of pumping a partial melt flow under a constant pressure and under the same pressure from individual pump to individual pump. It is therefore normal that these individual pumps are driven by a common drive shaft for all pumps. Known and standard is further the use of gear pumps because of the constancy of the delivery volume and delivery pressure.
Despite all efforts made to control the temperature and to meter of main melt flow and partial melt flows, differences between individual filaments are found over and over again.
In fact, attempts have become known from time to time, which had been directed to make the temperature control of the main melt flow uniform by mixing. To this end, the mixer disclosed in DE 12 36 479 B is used. Likewise known are many types of mixers, which are arranged on the extruder or installed as independent mixers in the melt flow (DE 20 30 756 C; U.S. Pat. No. 4,253,771; DE 20 40 919 A). However, these measures have been unable to eliminate the particularly serious problems of a uniform control of viscosity and temperature in the spinning of multifilament thermoplastic yarns. Likewise, it has not been possible to accomplish this by a mixer arranged upstream of the nozzle plate, such as is known from DE 16 60 674 A.
It is the object of the present invention to eliminate such differences in temperature and viscosity.
This object is accomplished by a spin system including a melt line transporting a main melt flow from an extruder, and a distributor pump which divides the main melt flow into partial melt flows for distribution to a spinneret. The distributor pump is preferably a multiple gear pump having several planetary shafts driven by a common drive shaft. One of the shafts extends into a mixing channel immediately upstream of the distributor pump and is provided with mixing elements. Accordingly, the melt is mixed to reduce any temperature gradients just before the main melt flow is divided into the partial melt flows.